In an effort to treat low back pain, surgeon have removed the degenerative disc and inserted a fusion cage into the disc space. In an effort to minimize the invasiveness of the fusion procedure, more recent efforts have focused upon forming the fusion cage in-situ by flowing a curable material into a balloon that has been placed into the disc space.
US Patent Publication 2004-0230309 (DePuy Spine) discloses an orthopedic device for implanting between adjacent vertebrae comprising: an arcuate balloon and a hardenable material within said balloon. In some embodiments, the balloon has a footprint that substantially corresponds to a perimeter of a vertebral endplate. An inflatable device is inserted through a cannula into an intervertebral space and oriented so that, upon expansion, a natural angle between vertebrae will be at least partially restored. At least one component selected from the group consisting of a load-bearing component and an osteobiologic component is directed into the inflatable device through a fluid communication means. The FIG. 6B thereof discloses adjacent balloons in a disc space.
U.S. Pat. No. 8,007,535 (Hudgins) discloses an injectable annular ring useful in treating a deteriorating spinal disc. When used, the annular ring may be collapsed or folded in order for it to be placed through a small opening in a prepared intervertebral space within the annulus using minimally invasive techniques. Deployment or unfolding the ring in the intervertebral space provides an interior cavity bordered by the ring that is in direct contact with the vertebral endplates. When an internal volume of the ring is injected or filled with a load-bearing, hardenable material, the filled ring maintains the intervertebral spacing and prevents the ring from being expelled from the interior cavity through the small annular opening.
U.S. Pat. No. 6,332,894 (Stalcup) discloses an orthopaedic implant for implanting between adjacent vertebrae and a spine, includes a generally annular bag; and a hardened polymer within the bag. The method of fusing adjacent vertebrae in a spine includes the steps of forming an access hole in an annulus of a disc between the adjacent vertebrae; removing the nucleus within the disc to form a cavity surrounded by the annulus; placing a generally annular bag within the cavity; filling the bag with a polymer; injecting bone particles into the cavity surrounded by the annular bag; and hardening the polymer.
US Published Patent Application 2003-0028251 (Mathews) discloses methods and instruments for preparing a disc space and for forming interbody devices therein. The instruments include distractors having enlargeable portions positionable in the disc space for distracting the disc space. The enlargeable portions can also provide form about or against which an interbody device of a first material is placed. A second material may be placed in the disc space previously occupied by the distractors.
US Published Patent Application 2005-0119752 (Williams) discloses devices and methods for manufacturing devices for treating degenerated and/or traumatized intervertebral discs. Artificial discs and components of discs may include an artificial nucleus and/or an artificial annulus and may be comprised of shape memory materials synthesized to achieve desired mechanical and physical properties. An artificial nucleus and/or annulus according to the invention may comprise one or more hollow bodies that may be filled with a curable material for deployment. A hollow body according to the invention may comprise one or more partitions to define one or more chambers and may comprise means for directing the flow of material within said hollow body. FIG. 19a of Williams discloses a two-balloon design comprising a central balloon and a perimeter balloon.
Subsidence of an implanted interbody cage is a known risk in fusion and there is a higher occurrence for patients with lower bone density. Hou and Yuan, Spine Journal, 12, 3, 249-256 (2012) investigated the structural properties of lumbar endplates and reported that the periphery of the endplates particularly in the posterolateral region near the pedicles were significantly stronger than the central region. They also concluded that with increasing disc degeneration, the central region became weaker while minimal strength changes were observed in the peripheral region.